Fingerprints made visible with ink, artwork from Dr Henry Faulds's Guide to Finger-print Identification, 1905. Faulds, a Scottish scientist, was an early developer of fingerprint analysis. Convinced that the patterns of ridges on fingertips were unique, he set about trying to develop a system of analysis. Before prints left on objects could be compared to print of suspects, they had to be rendered visible. Shown here are greasy smudges made on paper and treated with ink. The two prints on the left were simply treated with ink, the print at top right treated with copying ink from printing presses, and the lower right print treated with diluted ink.